Neisseria gonorrhoeae causes a variety of disease syndromes including pelvic iniflammatory disease [PID]. PID can lead to chronic pelvic pain, ectopic pregnancy and infertility. Those syndromes caused by N. gonorrhoeae have, in common, intense inflammation mediated by inflammatory cells. This inflammation is primarily the result of the interaction of neisserial LPS (LOS) v\/ith the LPS receptor complex: TLR4 and MD- 2. The components of the LPS receptor were identified a decade ago, yet it is still poorly understood, 1) how the binding of lipid A to MD-2 results in the formation of an active receptor complex, and, 2) how a signal is subsequently transmitted resulting in the production of proinflammatory mediators such as TNFa and IL-ip. In this proposal, we describe plans to determine how MD-2, once bound to lipid A, acquires the ability to activate TLR4. The approach builds upon our success in purifying MD-2, a small molecule with 7 cysteine residues that has a notorious tendency to form inactive multimers. We plan to resolve the structure of MD-2 in the absence and presence of activating ligand, and in the presence of TLR4 to determine what conformational changes in TLR4/MD-2 induce signaling. We shall then focus our energies on TLR4-related adapter molecules involved in cell signaling. We have previously analyzed 5 single nucleotide polymorphisms (SNPs) in the adapter protein known as Mai (used by both TLR2 and TLR4). Two SNPs are of great interest: S180L and D96N. As part of another NIH funded project, we have begun to generate mice carrying these lesions and are screening patient samples for the presence of D96N. Mai knock out mice and knock-in mice carrying the mouse equivalent of D96N or S180L will be tested in the mouse model of GC infection by Dr. Ingalls (PI, project 2). We will perform similar molecular genetic studies of the 6 known SNPs in MyD88, the downstream adapter that interacts with Mai and an important adapter for at least 8 of the TLRs. Should any of the SNPs display a phenotype, we will generate knock-in mice and screen patient samples to determine relevancy. Finally, we will attempt to define the interaction of Mai and MyD88 by biochemical means, culminating in an attempt to co crystallize the Mal/MyD88 dimer.